Preparation of anhydrides by the use of ketene



V Patented Nov. 7, 1939 i PATENT OFFICE PREPARATION or annrnamns nr'rnn USE or KETENE Anthony H. Gleason, Elizabe to Standard Oil Development poration of Delaware No Drawing. Original 1931, Serial No. 556,

th, N. .L, assignor ompany, a, corapplic ati on August 13, 94.0. Divided and this application Marcli 6, 1936, Serial No. 67,417

23 Claims.

The present invention relates toimprovements in the manufacture of organic compounds of the type of acid anhydrides. The invention also includes improvements in the recovery of such compounds and the production of useful commercial products therefrom.

This application is a division of Steik, Gleason and Wiezevich application Serial No. 556,940, filed August .13, 1931, Patent No. 2,099,909.

The invention has for one of its principal objects a process of making acid anhydrides by the treatment of organic acids having more than two carbon atoms and having a boiling point above 130 C. with ketene or its polymers, and the separation of the compounds so formed.

Further objects of the invention will appear as the description proceeds.

Organic acids having more than two carbon atoms and having a boiling point above 130 C. upon being treated at ordinary temperatures (such as 20 C.) with ketene, enter into a chem- 'ical reaction, which is generally manifested by the liberation of heat. The reaction which occurs consists in the addition of the ketene tothe organic 'acid with the resulting formation of an aceto-organic acid mixed anhydride, probably according to the following equation:

Acid ketene mixed anhydride where R is an alkyl radical containing two or more carbon atoms. Such mixed anhydrides are formed by reacting ketene with an organic carboxylic acid other than acetic acid. a

The product so formed is relatively unstable, being easily decomposed by heat to yield'an or- 0n subjecting the mixed anhydride to heatand distillation at atmospheric pressure or ata pressure lower than atmospheric, acetic anhydride is separated in the form of a vapor, and is con- 86 densed. The residual acid anhydride obtained in provided to maintain a uniform temperature of about 20 C. The resulting mixed anhydride of the distillation is removed as bottoms. It is more reactive than the corresponding acid and may be used directly to esterify hydroxy compounds such as alcohols, cellulose, glycols, etc, or to acetylate amino compounds such as aniline, benzylaniline,- etc. Neutral solvents such .as ethyl ether, acetone, etc., may be used to keep the organic acid in solution, especially when the acids treated are solids or very viscous liquids. These solvents are generally recovered before the distillation of the acid anhydrides. Aliphatic, cyclic or heterocyclic organic acids are used to react withketene in the above reactions.

The method described above mentions the treatment of a single organic acid. However, a mixture of two or more organic acids may be treated in a like manner and after removal of the solvent and acetic anhydride, may be fractionated into the separate anhydrides, or use as a mixture of anhydrides. Polybasic organic acids may be used in a like manner.

.Organic acids containing the hydroxyl or amino groups, upon treatment with ketene at ordinary temperatures form the mixed anhydrides of the corresponding ester or acetamino derivatives. For instance, upon treating an organic hydroxy acid with ketene, the ketene reacts with the hydroxyl group forming an ester and adds to the carboxyl group, theresulting compound formed being a mixed ester anhydride of the organic hydroxy acid and acetic acid. Upon heating, the relatively unstable mixed ester anhydride of the organic acid is decomposed to acetic anhydride 'and the corresponding ester anhydride. These are then separated by distillation as described previously.

The following examples are given merely to illustrate the invention andare not to be regarded as limiting the invention in any respect.

Ketene vapors are passed through a liquid 40 organic acid such as a naphthenic acid or an aliphatic acid such as valeric acid at ordinary tem-' perature until no further action takes place". A rapid evolution of heat occurs during the reaction and suitable cooling means are preferably the naphthenic or valeric acid and acetic acid is subjected to a temperature above 130 Cato decompose the mixed anhydride and the acetic anhydride formed is distilled off from the remaining anhydride of naphthenic or valeric acid. Naphthenic acids, such as those present in petroleum, are converted almost quantitatively to the corresponding anhydrides by this treatment.

Organic hydroxy acids such as tartaric, lactic, or citric acids are dissolved in a neutral solvent such as ethyl ether, acetone, etc. This solution of the hydroxy acid is subjected to a treatment with ketene. A rapid evolution of heat takes place during the reaction and suitable cooling means are provided to maintain substantially low temperature. Four mols of ketene are absorbed per mol of acid in the case of tartaric or citric acid. The resulting mixed ester anhydrides of tartaric, lactic or citric acid and acetic acid are subjected to heat treatment at a temperature about 130 C. The neutral solvent is. volatilized and condensed. Theremaining mixture of acetic anhydride and mixed ester anhydrides of tartaric, lactic or citric acid is subjected to distillation and the acetic anhydride is converted into a vapor and condensed. The mixed ester anhydride of tartaric, lactic, or citric acid is recovered as bottoms in the distillation.

Glycine, which is an amino aliphatic acid having the formula CH2(NH2) COOH, is reacted with ketene in a similar manner. Upon heating and fractionating off the acetic anhydride, a residue is recovered consisting mainly of a diacetylamino acetic anhydride having the formula (CHzNHCOCHaCO) 2O Furoic acid under similar treatment is converted to furoic anhydride, pyridine carboxylic acids to pyridine carboxylic anhydrides, and hydroxy toluic acids to diacetyl tolyl anhydrides. Anthranilic acid is changed to anthranil (which is used in the synthesis of indigo), while the corresponding meta or para compounds are converted to diacetyl-amino benzoic anhydrides. Benzoic acid is likewise converted to benzoic anhydride. The process is not limited to unsubstituted acids but is also applicable to hydroxy and amino aliphatic, cyclic and heterocyclic acid. Acids of these types containing groups which do not react with ketene may also be used.

The temperature at which the ketene is absorbed is preferably around 20 C. in most cases, as stated above. However, variations are permissible provided that the heat of reaction is not sufiicient to prevent the formation of the desired compounds. In the stage of separating the products formed by the ketene absorption, a temperature is preferably employed just above that which is suflicient to distill off the lower boiling of the products, leaving .the residual products in the still. It is within the scope of the invention, however, to distill over the products and fractionally condense them. Any desired means of further purification of the products may be employed.

It will be understood that the foregoing description is merely illustrative of the invention, and that various changes and alternative pro cedures and proportions may be adopted within the scope of the appended claims, in which it is my intention to claim all novelty inherent in the invention as broadly as the prior art permits.

I claim:

1. A process of preparing acid anhydrides which comprises reacting a ketene with a carboxylic acid containing at least two carbon atoms and containing a different number of car'- bon atoms than the ketene, in a quantity sufiicient to react with any free acid radical and any reactive substituent which may be present, and

heating the reaction mixture so as to obtain an anhydride of said carboxylic acid.

2. A process of preparing acid anhydrides which comprises reacting a ketene with an allphatic carboxylic acid containing more than two carbon atoms in a quantity sufiicient to react with any free acid radical and any reactive substituent which may be present, and heating the reaction mixture so .as to obtain an anhydride of said carboxylic acid.

3. A process of preparing acid anhydrides which comprises reacting CH2=C=O with a saturated aliphatic carboxylic acid containing more than two carbon atoms in a quantitysuflicient to react with any free acid radical and any reactive substituent which may be present, and heating the reaction mixture so as to obtain an anhydride of said carboxylic acid.

4. A process of preparing acid anhydrides which comprises reacting CH2=C=O with a carboxylic acid containing more thantwo carbon atoms in a quantity sufficient to react with any free acid radical and any reactive substituent which may be present, heating the reaction mixture and distilling off acetic anhydride.

5. A process of preparing acid anhydrides which comprises reacting CH2=C=O in the gaseous state with a substantially anhydrous carboxylic acid containing more than two carbon atoms in a quantity suflicient to react with any free acid radical and any reactive substituent which may be present, heating the reaction mixture and distilling ofi acetic anhydride.

6. The method of producing anhydrides which comprises reacting ketene with carboxylic acids having more than 2 carbon atoms and heating the product sufliciently to decompose it into acetic anhydride and another anhydride.

'7. Method according to claim 6 in which a neutral solvent is employed.

8. Method according to claim 6 in which the products are subjected to distillation at pressure below atmospheric.

9. Method according to claim 6 carried out at ordinary temperature.

10. Method according to claim 6 in which the acid is an aliphatic acid.

11. Method according to claim 6 in which the acid contains a substituted group selected from the class consisting of hydroxy and amino groups.

12. The method of producing acetic anhydride and valeric anhydride which comprises reacting ketene with valeric acid and heating the product to a temperature above about 130 C. to decompose it into a mixture of acetic and valeric anhydrides.

13. The method of producing acid anhydrides and mixed esteranhydrides which comprises reacting ketene with an unsubstituted carboxylic acid and a carboxylic acid having a substituted group selected from the class consisting of hydroxy and amino groups, whereby the acids are converted into anhydrides and separating the resulting acid anhydride and mixed ester anhydride product.

14. Process for the preparation of mixed anhydrides, comprising reacting ketene with an or ganic carboxylic acid other than acetic acid.

15. A process of preparing acid anhydrides which comprises reacting a ketene with an aromatic carboxylic acid containing a different number of carbon atoms than the ketene in a quantity suflicient to react with any free acid radical and any reactive substituent which may be present, and heating the reaction mixture so as to obtain an anhydride of said carboxylic acid.

16. A process of preparing acid anhydrides which comprises reacting a ketene with an aliphatic carboxylic acid containing at least two carbon atoms and containing a different number of carbon atoms than the ketene in a quantity sufiicient to react substituent which may be present, and heating the reaction mixture so as to obtain an anhydride of said carboxylic acid.

1'7. A process of preparing acid anhydrides which comprises reacting a ketene with a saturated aliphatic carboxylic acid containing at least two carbon atoms and containing a difierent number of carbon atoms than the ketene in a quantity sufficient to react with any free acid radical and any reactive substituent which may be present, and heating the reaction mixture so as to obtain an anhydride of said carboxylic acid.

18. A process of preparing acid anhydride which comprises reacting a. ketene in the gaseous state witha substantially anhydrous carboxylic acid containing at least two carbon atoms and containing a difierent number of carbon atoms than the ketene in a quantity suflicient to different number of carbon atoms than the ketene in a quantity suflicient to react with any free acid radical and any reactive substituent which may be present, and heating the reaction mixture so as to obtain an anhydride of said carboxylic acid.

20. A process of preparing acid anhydrides which comprises reacting a ketene with an uning more than two carbon atoms in a quantitysufiicient to react with any free acid radical and any reactive substituent which may be present, and heating the reaction mixture so as to obtain an anhydride of said carboxylic acid.

21. A process of preparing acid anhydrides which comprises reacting a ketene with an unsubstituted hydrocarbon monocarboxylic acid containing at least two carbon atoms and containing a different number of carbon atoms than the ketene in a quantity suflicient to react with any free acid radical and any reactive substituent which may be present, and heating the reaction mixture so as to obtain an anhydride of said carboxylic acid.

22. Process for the preparation of mixed anhydrides, comprising reacting a ketene with an.

organic carboxylic acid other than acetic acid.

23. Process for the preparation of mixed anhydrides, comprising reacting a ketene with an organic carboxylic acid other than acetic acid at- 

